ESTRO 36 Abstract Book

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S842 ESTRO 36 2017
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To evaluate conformity, homogeneity and dose
distribution to PTV and organ at risk (OAR) of three
different types of radiotherapy techniques in pancreatic
cancer.
Material and Methods
Three radiotherapy treatment plans, including 3DCRT,
forward-planning IMRT and volumetric arc therapy (VMAT)
were created for 18 consecutive patients with pancreatic
cancer. Eight postoperative patients with a resectable
pancreatic cancer and ten patients with unresectable
locally advanced disease were selected for this dosimetric
analysis. Dose Volume Histogram (DVH) comparative
analysis was performed for PTV and OAR. Paired t-test was
used for statistical analysis.
Results
All plans exhibited similar PTV coverage (V95%) and
conformity (all p > 0.05). The Homogeneity Index (HI) was
acceptable for all plans; in particular, it was higher in
VMAT plans than in 3D-CRT and IMRT plans. The mean dose
to the liver was 13.5 Gy for 3D, 12.1 Gy for IMRT, 10.9 Gy
for VMAT (p<0.001) to the benefit of VMAT. Volumes of
kidneys irradiated to doses of 20Gy (V20), 23Gy (V23),
28Gy (V28) by the VMAT plans were significantly less than
those of the IMRT and 3D-CRT plans. The volume of kidneys
irradiated to a dose of 12 Gy (V12) was not significantly
different comparing the three techniques. Mean of the
maximum point dose to spinal cord was better in VMAT
plans (3D-CRT vs IMRT vs VMAT, 30.6 Gy, 34.1 Gy, 26.5 Gy,
respectively; p<0.001).
Conclusion
VMAT can be a better option in treating pancreatic cancer
as compared to IMRT and 3D-CRT. The VMAT plans resulted
in equivalent or superior dose distribution with a reduction
in the dose to organ at risk.
EP-1582 Analysis of Risk of a Second Cancer from
Scattered Radiation in Acoustic Neuroma Treatment
Y. Oh1, D.O. Shin2, D.H. Shin3, W.K. Chung4, M. Chung4,
D.W. Kim4
1 Kyung Hee University Hospital at Gangdong, Research
Institute of Clinical Medicine, Seoul, Korea Republic of
2 Kyung Hee University Hospital, Department of Radiation
Oncology, Seoul, Korea Republic of
3 National Cancer Center, Proton Therapy Center,
Goyang, Korea Republic of
4 Kyung Hee University Hospital at Gangdong, Department
of Radiation Oncology, Seoul, Korea Republic of
Purpose or Objective
This study aimed to compare the risk of a secondary
cancer from scattered and leakage doses in patients
receiving intensity-modulated radiotherapy (IMRT),
volumetric modulated arc therapy (VMAT), stereotactic
radiosurgery (SRS), Proton therapy and Tomotheraphy.
Material and Methods
Acoustic neuroma patients were treated with IMRT, VMAT,
SRS, Proton therapy or Tomotheraphy. Their excess
relative risk (ERR), excess absolute risk (EAR), and lifetime
attributable risk (LAR) of a secondary cancer were
estimated using the corresponding secondary doses
measured at various organs by using radio-
photoluminescence glass dosimeters (RPLGD) placed
inside a humanoid phantom.
Results
When a prescription dose was delivered in the planning
target volume of the 4 patients, the highest organ
equivalent doses (OED) was calculated in to Proton
therapy, followed by SRS, VMAT, IMRT and Tomotherapy.
The OED decreased as the distance from the primary beam
increased. The thyroid received the highest OED compared
to other organs. A lifetime attributable risk evaluation
estimated that more than 0.03% of acoustic neuroma (AN)
patients would get radiation-induced cancer within 20
years of receiving radiation therapy.
Conclusion
The organ with the highest radiation-induced cancer risk
after radiation treatment for AN was the thyroid. We
found that the LAR could be increased by the transmitted
dose from the primary beam. No modality-specific
difference in radiation-induced cancer risk was observed in
our study.
EP-1583 Quantifying Plan Quality Metrics using
Conventional and Stereotactic dosimetric indices in
Lung SBRT
R. Yaparpalvi1, M. Garg1, W. Bodner1, J. Shen1, D.
Mynampati1, H. Kuo1, N. Ohri 1, J. Fox 1, A. Basavatia 1, S.
Kalnicki1, W. Tome1
1Montefiore Medical Center, radiation Oncology, bronx,
USA
Purpose or Objective
Several metrics have been proposed in literature for
evaluating treatment plan quality in conventional and
stereotactic planned dose distributions. In this study, we
utilized these metrics for characterizing and quantifying
Lung SBRT dose distributions. By applying various plan
quality metrics available in the literature, we sought to
not only characterize Lung SBRT target dose distributions
but also evaluate merits of these metrics as tools for lung
SBRT plan quality assessment.
Material and Methods
Treatment plans of 100 Lung SBRT patients treated in our
institution were retrospectively reviewed. Dose
calculations were performed using AAA algorithm with
heterogeneity correction. A literature review on published
plan quality metrics in the categories- coverage,
homogeneity, conformity and gradient was performed. For
each patient, using dose-volume histogram (DVH) data,
plan quality metric values were quantified. Data were
analyzed using descriptive statistics and two-tailed
probability t-test (Wilcoxon signed-rank test). A p-value of
< 0.05 was considered statistically significant.
Results
For the study, the mean (±SD) plan quality metrics in the
four representative categories were: Coverage (96.4 ±2.4
%); Homogeneity (0.21 ±0.06); Conformity (0.90 ±0.06)
and Gradient (1.27 ±0.30 cm). Geometric conformity
strongly correlated with conformity index (p<0.0001).
Gradient measures strongly correlated with target volume
(p<0.0001). The RTOG lung SBRT protocol advocated
conformity guidelines for prescribed dose in all categories
were met in ≥94% of cases. Evaluating High Dose Spillage,
the average cumulative volume of all tissue outside the
PTV receiving a dose of > 105% of prescription dose was
0.94 (± 1.64) %. Considering Low Dose Spillage, the
maximum % of prescription dose to any point at 2 cm
distance in any direction from PTV was 56.0 (± 11.4) %.
The proportion of lung volume (total lung volume – GTV)
receiving doses of 20 Gy and 5 Gy (V 20 and V 5) were mean
4.9 % (± 3.1) and 16.9 % (± 9.0), respectively.
Conclusion
Our study metrics are valuable tools for establishing lung
SBRT plan quality guidelines. Based on our data, we
recommend using the following metrics as surrogates for
establishing SBRT lung plan quality guidelines– Coverage %
(ICRU 62), Homogeneity (HIICRU83), Conformity (CN or
CIPaddick), and Gradient (R50% ).
EP-1584 Deformable image registration and dose
accumulation for arc-Total Body Irradiation
G. Guidi1, N. Maffei1, P. Ceroni1, G.M. Mistretta1, F.
Lohr2, T. Costi1
1Az. Ospedaliero Universitaria di Modena, Medical
Physics, Modena, Italy
2Az. Ospedaliero Universitaria di Modena, Radiation
Oncology, Modena, Italy
Purpose or Objective